Arc ion plating is a well-known technique which achieves its plating purpose through the deposition of metal particles evaporated by an electric arc in a vacuum. The electric arc is characterized by the formation of a cathode spot on the cathode surface, which contains the metal to be vaporized and deposited on an object or a part. In the arc ion plating terminology, the cathode surface is called a "target". An electric voltage above a threshold is required to sustain the electric arc between the anode and the cathode. During the arc ion plating process, the temperature at the cathode spot is approximately equal to the boiling point temperature of the depositing metal so as to allow substantial vapor pressure to be developed for the depositing metal which forms the cathode surface. The vapors produced from the cathode spots are then used to coat objects placed within the vacuum chamber and to sustain the arc ignited between the cathode and the anode. An inert ionizable gas can be introduced into the vacuum chamber to, in conjunction with the use of a triggering electrode, improve the generation as well as stabilizing of the electric arc. Likewise, a reactive gas can be introduced in the vacuum chamber to cause the precipitation of desired compound on the surface of the object being electric arc plated.
As the arc ion plating technique gets fine-tuned, several problems have surfaced. One of the most noticeable problems is the existence of macro particles, which, after they are deposited on the object, often cause the formation of locally roughened film surface. Such a roughened film surface not only projects a defective appearance, more importantly, it can also result in degradations in the mechanical properties of the finished product. For example, the product with roughened film surface tends to crack more easily.
U.S. Pat. No. 3,793,179, which discloses an apparatus for metal evaporation coating, taught many of the fundamental principle of the arc ion plating technique. The content thereof is incorporated herein by reference.
Several other subsequent prior art references have discussed modifications to improve the arc ion plating technology. For example, U.S. Pat. No. 4,673,477, the content thereof is incorporated herein by reference, discloses an apparatus for vacuum arc deposition of material on a surface of an object using a vacuum chamber accommodating the active surface of the cathode and an anode, wherein a power supply is connected to the anode and the cathode to establish an electric arc. The track of the arc is controlled with a magnetic field established with a permanent magnet that is moved in a closed path relative to the cathode.
U.S. Pat. No. 5,298,136, the content thereof is incorporated herein by reference, discloses an apparatus for controlled arc coating of substrates utilizing relatively thick cathodes (i.e., targets). The thick targets are capable of use by controlling and steering the arc in a desired path to produce coatings of the desired compositions using magnetic fields generated to provide arc path control and modulation for efficient cathode utilization.
The above-mentioned prior art references involved improvements in an efficient generation of the vaporized metal ions from the target (i.e., the cathode) surface by controlling the formation of and the disposition of the electric arc. At the present time, the metal particle generating component, i.e., the cathode-anode component, of the arc ion plating apparatus cannot effectively accommodate a very large object. The exit of the art ion generating chamber must be comparable in dimension with respect to the object so as to minimize inhomogeneity between the center and the two ends of the object. On the other hand, for a relatively small object, the metal particle generating component with a fixed dimension may at times cause unnecessary waste and result in loss in efficiency. Furthermore, while the prior art references discussed options to minimize the occurrence of macro particles, they involve relatively complicated design and may not be cost-effective.